Two Spaceships & Light: Measuring Speed from Earth

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SUMMARY

The discussion centers on the concept of light speed as measured from Earth when emitted from two spaceships passing each other. Both spaceships send light beams, one directed backward and the other forward, yet both are measured to travel at the constant speed of light, denoted as 'c'. This reinforces the principle that the speed of light remains invariant regardless of the relative motion of the source and observer, a fundamental tenet of Einstein's theory of relativity.

PREREQUISITES
  • Understanding of Einstein's theory of relativity
  • Familiarity with the concept of light speed (c)
  • Basic knowledge of inertial reference frames
  • Comprehension of the principles of simultaneity in physics
NEXT STEPS
  • Research the implications of Einstein's theory of relativity on time dilation
  • Explore the concept of simultaneity in different inertial frames
  • Study the experimental evidence supporting the constancy of light speed
  • Learn about the Lorentz transformations and their applications
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Physicists, students of physics, and anyone interested in the principles of relativity and the behavior of light in different reference frames.

keepitmoving
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two spaceships send a light beam toward Earth at the moment that they pass each other, one sends light backward toward us and one sends light forward toward us.
On Earth we measure the light speed as equal but let's back up to when the two lights were emitted. What speed would we measure for the two lights?
 
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c

They always measure c.
 

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